the environment of star formation theory: low-mass versus high-mass stars
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1) The environment of star formation
2) Theory: low-mass versus high-mass stars
3) The birthplaces of high-mass stars
4) Evolutionary scheme for high-mass stars
5) Conclusion: formation by accretion?
High-mass stars from cradle to first steps: a possible evolutionary sequence
(High-mass M*>10M⊙ L*>104L⊙ B3-O)
The environment of star formation
• Clouds: 10100 pc; 10 K; 10103 cm-3; Av=110; CO,13CO; nCO/nH2
=10-4
• Clumps: 1 pc; 50 K; 105 cm-3; AV=100; CS, C34S; nCS/nH2
=10-8
• Cores: 0.1 pc; 100 K; 107 cm-3; Av=1000; CH3CN, exotic species; nCH3CN/nH2
=10-10
• YSOs signposts: IRAS, masers, UC HIIs
Low-mass VS High-mass
“Standard” (Shu’s) picture:Accretion onto protostarStatic envelope: nR-2
Infalling region: nR-3/2
Protostar: tKH=GM2/R*L*
Accretion: tacc=(dMacc/dt)/M*
– Low-mass stars: tKH > tacc
– High-mass stars: tKH < tacc
High-mass stars reach ZAMS still accreting
Low-mass VS High-mass
“Standard” (Shu’s) picture:Accretion onto protostarStatic envelope: nR-2
Infalling region: nR-3/2
Protostar: tKH=GM2/R*L*
Accretion: tacc=(dMacc/dt)/M*
– Low-mass stars: tKH > tacc
– High-mass stars: tKH < tacc
High-mass stars reach ZAMS still accreting
Problem:Stellar winds + radiation pressure stop accretion at
M*=8 M⊙ how can M*>8 M⊙ form?
Solutions:i. Accretion with
dM/dt(High-M*)>>dM/dt(Low-M*)=10-5 M⊙/yii. Accretion through disks (+outflows)iii. Merging of many low-mass stars
Observations of the natal environment of high-mass stars are necessary to solve this problem!
The search for high-mass YSOsHigh-mass YSOs deeply embedded observations more
difficult than for low-mass YSOs (e.g. S254/7 SFR)Observational problem: to find suitable tracer and target1) What to look for? High-density, high-temper. tracers
high-excitation lines, rare molecules, (sub)mm continuum
2) Where to search for? Young and massive targets:a) UC HIIs: OB stars are in clusters
b) H2O masers without free-free: luminous but without UC HII region
c) IRAS without H2O and UC HII: protostellar phase?
The search for high-mass YSOsHigh-mass YSOs deeply embedded observations more
difficult than for low-mass YSOs (e.g. S254/7 SFR)Observational problem: to find suitable tracer and target1) What to look for? High-density, high-temper. tracers
high-excitation lines, rare molecules, (sub)mm continuum
2) Where to search for? Young and massive targets:a) UC HIIs: OB stars are in clusters
b) H2O masers without free-free: luminous but without UC HII region
c) IRAS without H2O and UC HII: protostellar phase?
Observations
High-mass YSOs: AV > 10 radioNIR needed
• Low angular resolution = single-dish = 10”2’ Effelsberg, Nobeyama, IRAM, JCMT, CSO, NRAO NH3, CO, 13CO, CS, C34S, CH3C2H, CN, HCO+, …
• High angular resolution = interferometers = 0.3”4” VLA, IRAM, Nobeyama, OVRO, BIMA, VLBI NH3, CH3CN, CH3OH, SiO, HCO+, H2O, continuum
General results
Targets surrounded by dense, medium size clumps: 1 pc, 50 K, 105–106 cm-3, 103–104 M⊙
Dense, small cores found close to/around targets: 0.1 pc, >107 cm-3, 40–200 K, 10–103 M⊙
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Clumps
Traced by all molecules observed real entities!
• Mclump>Mvirial large B (1mG) needed for equilibrium
• TK R-0.5 heated by source close to centre
• nH2 R-2.6 marginally stable
• dMacc/dt = Mclump/tAD = 10-3–10-2 M⊙/y large accretion rates
clumps may be marginally stable entities (∼105 y) accretion from clumps feeds embedded YSOs
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L ⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L ⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L ⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Beuther et al. (2002)
Hot Cores (HCs)
Hot (100–200 K) cores often found close to UC HIIs:• H2O masers and high energy lines large nH2
and TK
• many rare molecules evaporation from dust grains• TK R-3/4 inner energy source• LIRAS 104 L⊙ embedded OB star• a few HCs contain UC HIIs! OB stars• rotating circumstellar disks found in some HCs• molecular outflows from several HCs
HCs host young ZAMS high-mass stars
Warm cores (WC)
Mostly towards IRAS sources with [25-12]<0.57 :
• warm (50 K) but dense and massive (10–102 M⊙)
• luminous (LIRAS 104 L⊙) high-mass YSOs
• few H2O masers (no OH masers) prior to HC phase
• no cm continuum emission hypercompact HII?• weak evidence for disks and outflows• interesting candidate: the case of G24.78+0.08
WCs may be “class 0” high-mass sources (?)
Warm cores (WC)
Mostly towards IRAS sources with [25-12]<0.57 :
• warm (50 K) but dense and massive (10–102 M⊙)
• luminous (LIRAS 104 L⊙) high-mass YSOs
• few H2O masers (no OH masers) prior to HC phase
• no cm continuum emission hypercompact HII?• weak evidence for disks and outflows• interesting candidate: the case of G24.78+0.08
WCs may be “class 0” high-mass sources (?)
H2O maser
Warm cores (WC)
Mostly towards IRAS sources with [25-12]<0.57 :
• warm (50 K) but dense and massive (10–102 M⊙)
• luminous (LIRAS 104 L⊙) high-mass YSOs
• few H2O masers (no OH masers) prior to HC phase
• no cm continuum emission hypercompact HII?• weak evidence for disks and outflows• interesting candidate: the case of G24.78+0.08
WCs may be “class 0” high-mass sources (?)
IRAS 23385+6053
Warm cores (WC)
Mostly towards IRAS sources with [25-12]<0.57 :
• warm (50 K) but dense and massive (10–102 M⊙)
• luminous (LIRAS 104 L⊙) high-mass YSOs
• few H2O masers (no OH masers) prior to HC phase
• no cm continuum emission hypercompact HII?• weak evidence for disks and outflows• interesting candidate: the case of G24.78+0.08
WCs may be “class 0” high-mass sources (?)
WC
HC
Warm cores (WC)
Mostly towards IRAS sources with [25-12]<0.57 :
• warm (50 K) but dense and massive (10–102 M⊙)
• luminous (LIRAS 104 L⊙) high-mass YSOs
• few H2O masers (no OH masers) prior to HC phase
• no cm continuum emission hypercompact HII?• weak evidence for disks and outflows• interesting candidate: the case of G24.78+0.08
WCs may be “class 0” high-mass sources (?)
Proposed evolutionary sequence
I. WC: dMacc/dt 10-5 M⊙/y squelches UC HII; e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
II. HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
III. HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
IV. HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
V. (UC)HII: HC is “evaporated”
IRAS 23385+6053
Proposed evolutionary sequence
I. WC: dMacc/dt 10-5 M⊙/y squelches UC HII; e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
II. HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
III. HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
IV. HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
V. (UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I. WC: dMacc/dt 10-5 M⊙/y squelches UC HII; e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
II. HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
III. HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
IV. HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
V. (UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I. WC: dMacc/dt 10-5 M⊙/y squelches UC HII; e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
II. HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
III. HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
IV. HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
V. (UC)HII: HC is “evaporated”
Proposed evolutionary sequence
I. WC: dMacc/dt 10-5 M⊙/y squelches UC HII; e.g. IRAS 23385+6053: 104 L⊙, 40 K, 370 M⊙
II. HC: outflow+disk, non-spherical accretion? e.g. IRAS 20126+4104: 104 L⊙, 200 K, 10 M⊙
III. HC+ small UC HII: outflow+disk remnant, UC HII begins expansion; e.g. G10.47+0.03: 5 105 L⊙, 200 K, 103 M⊙
IV. HC+UC HII: outflow remnant, UC HII destroys HC; e.g. G5.89-0.39: 7 105 L⊙, 100 K, 3 103 M⊙
V. (UC)HII: HC is “evaporated”
Conclusions
High-mass YSOs are associated with:
• large accretion rates
• outflows and circumstellar disks
High-mass stars could form through accretion as much as low-mass stars
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